WASHINGTON — A U.S. official said today that American fighter jets and drones have done nearly a dozen airstrikes in Iraq since Tuesday, even as Islamic State militants threatened to kill a second American captive in retribution for any continued strikes. The militants released a video Tuesday showing U.S. journalist James Foley being beheaded. The official says the airstrikes were in the area of the Mosul Dam and were aimed at helping Iraqi and Kurdish forces create a buffer zone at the key facility. The strikes have helped Iraqi and Kurdish troops reclaim the dam from the insurgents. The militants threatened to kill a second American journalist, Steven Sotloff, who is being held captive in case of airstrikes. Also, the The White House says President Barack Obama will deliver a statement today. The White House isn’t saying what topics Obama will address. But the statement comes as the White House is saying that U.S. intelligence officials have determined the video showing the execution of Foley is authentic. Obama will speak from Martha’s Vineyard in Massachusetts, where he’s in the second week of his annual summer vacation.